STUDIES OF SPORE DISSEMINATION OF VENTURIA 
INAEQUALIS (CKE.) WINT. IN RELATION TO SEASONAL 
DEVELOPMENT OF APPLE SCAB 1 
By C. N. Frey, 2 formerly Assistant in Plant Pathology , University of Wisconsin , 
and G. W. Keitt, Professor of Plant Pathology , University of Wisconsin 
During the season of 1916 it became 
apparent to the junior author, who was 
then beginning work on the control of 
apple scab, 3 that further studies of 
certain details of the life history of the 
causal fungus in relation to the sea¬ 
sonal development of the disease under 
local conditions were fundamental to 
the satisfactory application of control 
measures. A clearer understanding of 
certain aspects of spore dissemination 
and infection appeared to be of primary 
importance. Accordingly, in the spring 
and summer of 1917, some studies of 
these questions were undertaken as a 
minor problem in such time as the 
writers could devote to it. The advent 
of the war prevented continuation of 
this work, and subsequently pressure of 
duties in another field upon the senior 
author has prevented earlier publica¬ 
tion of the results. However, the 
junior author and his coworkers have 
extended these investigations and plan 
to supplement the following account in 
a later paper. 
A STUDY OF THE SPORE CONTENT 
OF ORCHARD AIR 
METHODS 
Of the various methods for the study 
of spore dissemination described in the 
literature with which the writers are 
conversant, none appeared exactly to 
meet the requirements of their problem. 
Consequently an attempt was made to 
devise one. 
ELECTRICAL PRECIPITATION 
At the suggestion of L. F. Hawley of 
the Forest Products Laboratory of the 
United States Department of Agricul¬ 
ture, an attempt was made to adapt to 
the purposes of the present study the 
electrical method described by Cottrell 4 
for removing suspended particles from 
gases. Preliminary experiments showed 
that when spores of Venturia inaequalis 
Ustilago zeae , or certain other organisms 
were brought within the field of a static 
machine most of them became nega¬ 
tively charged and passed to the positive 
pole. A few of the spores tested be¬ 
came positively charged, a small num¬ 
ber of each kind always passing to the 
negative pole. 
These observations encouraged the 
writers to pursue their experiments 
somewhat ffarther. A glass tube 12 
inches long and 1.5 inches in diameter 
was set up between the poles of the 
static machine. In each end of this 
tube was placed a rubber stopper 
through which ran two glass tubes, 
each 2 inches long and one-fourth 
inch in diameter. One of these tubes 
was attached to a vacuum pump, 
while the opposite one was left open 
to permit the access of air. A copper 
wire was passed through the other 
two tubes in such manner as to run 
through the middle of the larger tube 
and to attach at one end to the nega¬ 
tive pole of the static machine. All 
openings into the larger tube were 
sealed with wax, with the exception 
of the two small tubes to permit the 
ingress and egress of air. Tin foil 
was lightly wrapped around the out¬ 
side of the large tube and connected 
with its inner wall. A copper wire 
attached to the foil was connected 
with the positive pole of the static 
machine. A thin coat of vaseline 
had previously been rubbed on the 
inside of the tube to aid in holding 
the spores as they were precipitated 
against it. Air currents bearing 
abundant fungus spores were then 
passed through the tube while the 
static machine was in operation. 
When the current of air was suitably 
regulated and the static machine 
delivered a high potential, about 
30,000 to 50,000 volts, most of the 
spores were caught on the first 3 or 4 
1 Received for publication May 24, 1924; issued June, 1925. Approved for publication by the Direc¬ 
tor of the Wisconsin Agricultural Experiment Station. 
2 Biochemist, Ward Baking Company, 103 W. 183d St., New York city. 
3 A comprehensive account of this disease and its causal fungus, Venturia inaequalis (Cke.) Wint., with 
an extensive bibliography, is given in the following citation: Wallace, E. scab disease of apples. 
N. Y. Cornell Agr. Exp. Sta. Bui. 335, p. 545-624, illus. 1913. 
4 Cottrell, F. G. the electrical precipitation of suspended particles. Jour. Indus, and Engin. 
Chem. 3 : 542-550, illus. 1911. 
Journal of Agricultural Research. 
Washington, D. C. 
( 529 ) 
Vol. XXX, No. 5 
Mar. 15, 1925 
Key No. Wis.-28 
